Chromosomes

Chromosome Abnormalities

• Numerical abnormalities

• Structural abnormalities

• Mixoploidy

Numerical Abnormalities

• Monosomy

• Trisomy

A. B. C.

Non-disjunction

Consequence of non-disjunction

• Trisomy

–(21) Down syndrome –(13) Patau syndrome–(18) Edward’s syndrome

Polyploidy• Addition of one or more entire set of chromosomes

Disorders of Chromosome Number

• Down Syndrome• Patau and Edwards Syndrome• Klinefelter Syndrome• Turner Syndrome• XXX Females and XYY Males

Down Syndrome

Down Syndrome• History– 1866 first clinically described by Dr.

Down– 1959 chromosomal basis discovered

• Incidence 1 in 691 births in the US– Majority of cases are diagnosed

prenatally (~60%)

• Prevalence: currently 400,000 in US

•

Patau Syndrome

Patau Syndrome

• Heart defects• Brain or spinal cord abnormalities• Weak muscle tone• Prognosis–45% die within few days/weeks–80% within 1st year

Edwards Syndromes

Edward’s syndrome• Clinical symptoms– Structural heart defects– Intestinal abnormalities–Breathing difficulties– Intellectual disability

• Prognosis–Median lifespan – 5-15 days– Longer than 1 year – 8%– Live to 10 years- 1%

Klinefelter Syndrome

Klinefelter Syndrome (XXY)• Incidence- 1 in 1000 live

male births

• Clinical features-– Lower than normal verbal

IQ– Infertility

• Testosterone treatment

Turner’s Syndrome

Turner Syndrome (X)• Incidence- 1 in 5000 – 10,000

female births

• Clinical features– Loss of ovarian function– Normal intelligence– Developmental delay– Learning disability

• Estrogen treatment from puberty on

https://www.youtube.com/results?search_query=turner

%27s+syndrome&sm=3